The invention relates to a process for the sulfur vulcanization of aqueous dispersions of unsaturated polymers and in particular to the use of dithiocarboxylic acids or their salts as vulcanization accelerators. Optionally, the vulcanization is performed in the presence of other conventional additives. The process according to the invention makes possible the production of acceptable vulcanizates, with the avoidance of nitrosamines, which are considered health risks according to present knowledge.
Both the new hazardous materials decree and the new TRGS 522 "Nitrosamines" (Technical Rules for Hazardous Materials) confront producers and processors in the rubber industry with the task of reducing nitrosamine concentrations. There is agreement that this is to be achieved only with the avoidance of potential nitrosamine sources. But potential nitrosamine sources are the most important vulcanization accelerators in use. (See Kautschuk und Gummi--Kunststoffe 42, 1/89, page 16 ff.).
The vulcanization of latex items, such as, e.g., mattresses, rubberized hair curlers, shoe components or carpet undercoatings, takes place because of the presence of water mainly at temperatures less than or equal to 100.degree. C. To achieve a sufficient crosslinking density and a high vulcanization rate, the vulcanization is performed with accelerator combinations which almost always contain dialkylzinc dithiocarbamates. In the course of the vulcanization process, these disintegrate into amines, which react with the omnipresent (NO).sub.x to nitrosamines. These nitrosamines, which are considered health risks according to present knowledge (cf. Umschau 1985 (1), 24), can be detected in the ambient air of the production units.
Nitrogen-free vulcanization accelerators are known, e.g., in the form of xanthates and dithiophosphates. However, they are not effective at low vulcanization temperatures and, therefore, are not used. It is known to vulcanize solid rubber with aromatic hydroxydithiocarboxylic acids or their salts. But in this case, the vulcanization takes place at temperatures greater than or equal to 100.degree. C., preferably between 120.degree. and 240.degree. C. (See German Patent Appln. P 39 41 001.3).